/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
#include <iostream>
#include <stack>

using namespace std;

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;

    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class Solution {
public:
    TreeNode *lowestCommonAncestor(TreeNode *root, TreeNode *p, TreeNode *q) {
        if (root == NULL || root == p || root == q) return root;
        TreeNode *l = lowestCommonAncestor(root->left, p, q);
        TreeNode *r = lowestCommonAncestor(root->right, p, q);
        if (l != NULL && r != NULL)return root;
        return l ? l : r;
    }
};